NEED BIG BRAINS!!! can anyone help me understand Class D amplifiers?

[knifemyglitter]

hi everyone. I have a 26 page paper on Class D amplifiers due and i need as much info as possible. If anyone understands them in detail, id be forever thankful to you if you could help me out, or if you could help find companies that i could contact and they could send me the appropriate powerpoint info. Thanks!

Kevin A.

 

[f95toli]

Look at Bang&Olufsens website. They have some white papers you can download (that are full of control theory).
B&O make the ICEPower modules, used not only by them but also by several other companies.
Most of the big asian companies also have class-D amps in their ranges (usually in AV-recievers), Panasonic and Sony comes to mind.

 

[bobsmith1492]

It's a simple theory, similar to that of a switching power supply. Your output transistors are either on or off; switch them on and off really fast, and the average voltage is your output voltage. This is known as PWM, pulse-width modulation. Filter the high-frequency switching noise out, and you have your desired signal. The benefit is that, since the output transistors are always on or off, they dissipate, theoretically, no power (except their inherent on-resistance, which is extremely low for a good MOSFET).

That's the basic concept... how in-depth are you looking for? I was looking into building one from discrete parts, which really doesn't require that much. Just run a high-speed triangle wave and your audio signal into a comparator; switch the output MOSFETS with the output from that comparator. That gets you simple PWM. Then there's the design of the output topology to look at (really you need a high and a low side FET) and the output filter (the intended load comes into effect here).

Google around; that's what I did, so much else would just be doing your work for you.

 

[knifemyglitter]

bob, thank you very much for the insight. as far as how in-depth i have to go into....well, about as far in depth as humanly possible, i have to fill up 26 friggin pages with this. Ive tried contacting SPL and T.I. and i think im gonna try Sony and panasonic as the fellow mentioned above, but if you can name any more, thatd be great.

Kevin A.

 

[f95toli]

Did you look at
http://www.icepower.bang-olufsen.com
as I suggested?

If you follow the "download"-link on that page you will find all sorts of technical documents (including various AES articles), you could easily fll 260 pages just by using that information.
Note that B&O developed much of the technology behind modern class-D amps (the basic principle has been known for a long time but was rarely used in non-PA systems), their initial R&D was essentially basic (as in academic) research done in collaboration with various universites around Europe.

 

[Twinpeaksr]

Search Sound and Vision Website, they had an article a while (1yr?) ago about the differences between A, B, And D amplifiers. I believe that National Semi and Maxim also make Class D amplifiers. It also defines why it has only been recently that they have been able to make them work for audio.

As was explained they are pretty simple, if you want 26 pages, I suggest a bigger font, or you can derive Maxwell Equations, that is always a fun one.

 

[f95toli]

Originally posted by: Twinpeaksr

As was explained they are pretty simple, if you want 26 pages, I suggest a bigger font, or you can derive Maxwell Equations, that is always a fun one.

While the principle behind class D amps is simple real amplifiers are actually pretty complicated. There is a reason why there are so few good DIY class-D amps around (you can find lots of projects, but most of the them us amp modules from e.g. B&O or ColdAmp).
Note that "complicated" does not neccesarily mean "many components.", it is more a case being able to calculate e.g. the exact components values etc; if you get it wrong all sort of weird things might happen. The type of "trial-end-error" that you can get away with when designing class A and A/B amp doesn't really work here. Also, the frequencies involved are rather hight meaning the PCB-design is far from trivial.

There is a reason why the B&O white papers and articles are full of control theory; you don't want any poles in the RHP when you are building an amp which can deliver a 1kW into 8 Ohms...

 

[bobsmith1492]

Originally posted by: f95toli

Originally posted by: Twinpeaksr

As was explained they are pretty simple, if you want 26 pages, I suggest a bigger font, or you can derive Maxwell Equations, that is always a fun one.

While the principle behind class D amps is simple real amplifiers are actually pretty complicated. There is a reason why there are so few good DIY class-D amps around (you can find lots of projects, but most of the them us amp modules from e.g. B&O or ColdAmp).
Note that "complicated" does not neccesarily mean "many components.", it is more a case being able to calculate e.g. the exact components values etc; if you get it wrong all sort of weird things might happen. The type of "trial-end-error" that you can get away with when designing class A and A/B amp doesn't really work here. Also, the frequencies involved are rather hight meaning the PCB-design is far from trivial.

There is a reason why the B&O white papers and articles are full of control theory; you don't want any poles in the RHP when you are building an amp which can deliver a 1kW into 8 Ohms...

Oh, but it would be so fun! 1kW of pure DC into a wire.... mmmm.... love the smell of smoke in the morning.

Off-topic, I was thinking about getting a Tripath switching amp module, but have no idea of how to get one. They're pretty interesting looking, but a friend of mine says the one he build doesn't really hit their advertised specs, unsurprisingly.